Foam heating system

ABSTRACT

A foam assembly system is provided. The system is configured to heat a surface of foam. After the heating of the foam, an adhesive is applied, typically a high solids adhesive. The foam is then bonded to another foam surface. It has been found that the pre-heating of the foam before adhesive application greatly enhances the bond strength between the foam and the second foam surface to which it is adhered.

BACKGROUND

In foam assembly processes, such as foam mattress assembly, water basedadhesives provide a safe, effective, and non-hazardous solution forbonding foam pieces together. However, many water based adhesivescontain a large percentage of water. Therefore if a foam assembly bondedwith water-based adhesives is packaged before fully dried, mold,unpleasant odors, substrate material breakdown, and the like maydevelop.

In particular, in foam mattress assembly and other assembled foamproducts, a fast growing trend in industry is to compress saidassemblies into a box that may be shipped directly to customers. Theboxes are sized such that traditional package shipping companies canhandle them. These foam assemblies are constructed, and then enclosed inan impermeable plastic bag which is vacuumed and compressed so that itfits into the shipping boxes. Vacuuming alone to compress the packagedoes not adequately extract water from the package, so trapped moistureis a common occurrence. Currently, the primary solution for this problemis to simply let the assemblies rest for a certain time period afterconstruction to let moisture evaporate. However, this slows down themanufacturing and shipping process, and requires extra storage space atthe manufacturing site.

One solution to minimize the presence of water or other solvents is touse a high solids adhesive, such as that in the range of 60% or moresolids, typically 60-80% solids. However, high solids adhesives do nothave sufficient wet tack for many foam assembly processes. Wet tackallows adhesive to rapidly hold the foam pieces together during assemblyand also allows for some stretching of the foam when making theassembly. Further still, high solids adhesives do not provide a strongenough bond between foam elements to achieve foam tear when processingat room temperature.

Therefore, what is needed is a system that may allow for enhancedprocessing of foam assembly components and adhesives to allow for use ofa high solids adhesive that achieves foam tear level adhesion of foamcomponents.

SUMMARY

The subject matter of this application may involve, in some cases,interrelated products, alternative solutions to a particular problem,and/or a plurality of different uses of a single system or article.

In one aspect, the present invention involves a system and method forheating a surface of a foam piece before adhesive is applied to thesurface a second foam surface is then adhered to the foam piece. Thissystem results in better reception of the adhesive by the foam, enhancesthe wet tack of the adhesive, and forms superior final bonds for thefoam assemblies having foam adhered together when compared to processingusing similar adhesives at ambient conditions.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 provides a side view of a foam assembly system of the presentinvention.

DETAILED DESCRIPTION

The present invention concerns an apparatus to minimize or eliminatewater from a foam assembly that also achieves very good bond strengthbetween foam layers.

The present invention involves a system and method for heating a surfaceof a foam (referred to as “preheating the foam:”), applying an adhesive,such as a high solids adhesive (used herein to refer to adhesives havinggreater than approximately 60% solids), to the heated surface of thefoam, and then applying a second foam surface to the heated surfacehaving adhesive on it. As such, the two foam surfaces may be adheredtogether, forming a foam assembly.

As used herein, a “foam assembly” may be any assembly that comprises twoor more foam pieces laminated together using an adhesive. It is evenpossible that a foam assembly may be a single foam element for example,by having two surfaces adhered together. Foam assemblies may be anysize, shape, foam type(s), and configuration, without straying from thescope of the present invention.

As used herein, the term “foam tear” means that adhesion between foamlayers is such that separation cannot occur without destruction(tearing) of the foam layers. This typically occurs in the form of deeptears—indicating very good adhesion, some tearing or shallowtearing-indicating moderate adhesion, or no tearing, indicatingincomplete adhesion.

As shown in FIG. 1, the present invention shows an embodiment of asystem using the inventive method contemplated herein. While thisembodiment is shown in an assembly conveyor embodiment, it should beunderstood that the invention may be carried out in steps without beingon a conveyor system without straying from the scope of this invention.Arrows D demonstrate the direction of travel of the foam piece 12 alongthe system. Initially, foam 12 is heated by a heat source 11, whichraises the temperature of a top surface 10 of the foam 12 above ambienttemperature. In one embodiment, the heat source 11 raises a surface 10temperature of the foam 12 to approximately 220-300 Fahrenheit, althoughdifferent temperatures may be achieved depending on embodiment. The foampiece 12 is then moved by a conveyor, rollers, or the like, or isotherwise physically moved to an adhesive application area. An adhesiveroller system 14, 15, 16, 17 is positioned down stream from the heatsource 11. The adhesive roller system includes a primary roller 16,secondary roller 15, support roller 14 and a trough 15 filled with theadhesive. The primary roller 16 rolls over the adhesive in trough 17,coating the roller 16 with adhesive, the primary roller 16 then appliesthis adhesive to the foam 12 beneath as it rolls over the heated surface10. It should be understood that while roll coating is used in thisFIGURE, any other adhesive application method (spraying, brushing,contact application, and the like) may be used without straying from thescope of the present invention. The adhesive typically may be a highsolids adhesive such as an adhesive having 60% solids, or 60-80% solids,but this is not required. After the coating of the adhesive on theheated foam surface, the foam layer 12 with adhesive applied is adheredto another foam layer 18. In the embodiment shown in the FIGURE, thefoam 12 having adhesive applied is flipped over and laminated to asecond core foam 18 so that the foam 12 top surface 10 is bonded tosecond foam core 18. In some embodiments, the two foam pieces 12, 18 maybe compressed together to enhance bonding, but that is not necessarilyrequired. Compression may be achieved by a force applying device thaturges the pieces 12, 18 towards each other; vacuum packaging the foamassembly, stacking the foam assembly on other assemblies; flipping theassembly if second core foam 18 is heavier than foam 12, and the like.

The heat source may be any structure capable of increasing thetemperature of a surface of foam. For example, a convection heat source,infra-red heat source, direct contact conduction heat source, and thelike. In a particular further embodiment, a fan or other air movingstructure may force air, such as heated air shown in FIG. 1 as 19,towards the foam.

The present invention has, in initial tests, provided drasticallyenhanced performance compared to the prior art methods of roll coatingadhesives on foam surfaces without any pre-heating. To test theeffectiveness of the present invention, tests were performed to comparebond strength of preheated foam of the present invention with ambienttreatment in the prior art. A high solids adhesive was applied with anadhesive roller to 12″×18″ pieces of 3 lb. viscoelastic foam which werethen adhered to conventional polyurethane core foam (such as mattresscore foam). Foam samples that were not preheated (marked as “N” in thepre-heated column) were heated after the adhesive was applied, and therewas no foam tear in two out of three of these samples, with the samplehaving tear using a high amount of adhesive and having only partialtear. Therefore, the step of heating the foam before adhesive is appliedcan be seen to be especially advantageous. Assembly was immediate afteradhesive application, and the two foam pieces were compressed togetherfor ten seconds.

TABLE 1 Comparison of Foam Tear Between Preheated and Non-heated FoamSurface Foam tear after 3 Preheated (Y/N) Temperature Dwell Time g/yd²hours Y 280° F. 30 sec 72 Deep Y 240° F. 20 sec 108 Deep Y 260° F. 10sec 72 Deep Y 270° F. 10 sec 72 Deep Y 260° F. 30 sec 72 Deep Y 230° F.10 sec 72 Deep N 160° F. 10 sec 72 None N 140° F.  5 sec 72 None N 140°F. 10 sec 108 Some

Table 2 shows results of varying heating dwell time (dwell time column);adhesive density (g/yd² column); varied foam types (Type of foamcolumn); wait time between adhesive application and assembly to thesecond foam surface (Time before assembly column); and the time requiredfor the adhesive to dry/cure sufficiently to provide foam tear (Timeuntil foam tear column). It can be seen in all foam preheatingembodiments that foam tear occurred within thirty minutes, and typicallymuch less than that. As with Table 1, the second foam is a conventionalpolyurethane core foam (such as mattress core foam) while the foamlaminated thereto (which is heated to the identified surfacetemperature, and then adhesive is applied) may vary. High solidsadhesives were applied to surfaces of 12″×12″ foam pieces.

TABLE 2 Foam Tear Timing under Different Conditions Type of foam TimeSurface Dwell laminated to before Time until Temperature Time g/yd² corefoam assembly foam tear. 245° F. 15 sec 50 Visco 40 sec  >6 min <35 min240° F. 15 sec 55 Visco Immed. <18 min 260° F. 15 sec 70 Polyurethane 40sec <20 min Foam-low permeability 240° F. 10 sec 70 Polyurethane 30 sec<10 min Foam-low permeability 280° F. 20 sec 70 Polyurethane Immed. <30min Foam-low permeability 240° F. 10 sec 70 Polyurethane Immed. <30 minFoam-low permeability 275° F. 20 sec 70 Polyurethane 60 sec  <7 minFoam-low permeability 240° F. 10 sec 70 Polyurethane 60 sec <10 minFoam-low permeability No preheat N/A 70 Polyurethane 60 sec <40 minFoam-low permeability

Table 3 provides further testing to determine when foam tear occurs. Inthis table, high solids adhesive is applied with an adhesive rollersystem to 12″×16″ 3 lb. viscoelastic foam. Samples were evaluated withinten minutes of assembly. Assembly of the two foam surfaces occurred 30seconds after adhesive application, with a ten second compression of thefoam surfaces towards each other after adhesion.

TABLE 3 Foam Tear Timing Based On Surface Temperature Surface Time untilfoam Preheated (Y/N) Temperature Dwell Time g/yd² tear Y 280° F. 30 sec54 4 min Y 280° F. 30 sec 54 5 min Y 255° F. 20 sec 54 7 min Y 250° F.20 sec 54 8 min Y 250° F. 20 sec 54 10 min 

In additional testing with low solids adhesive formulations, heating ofthe foam surface before adhesive application resulted in foam tear onehour after adhesion. By contrast, previous testing with non-preheatedfoam and a low solids adhesive formulation required approximately fourhours post drying before foam tear occurred.

As can be seen herein, preheating foam before adhesive application givesadhesive applied to the preheated foam both faster wet tack and faster,stronger bond development. The application of a high solids adhesivemeans that less water is added to the foam assembly than withtraditional water based adhesives.

While several variations of the present invention have been illustratedby way of example in preferred or particular embodiments, it is apparentthat further embodiments could be developed within the spirit and scopeof the present invention, or the inventive concept thereof. However, itis to be expressly understood that such modifications and adaptationsare within the spirit and scope of the present invention.

What is claimed is:
 1. A method of foam assembly comprising the stepsof: conveying a piece of foam along a conveyor; heating a top surface ofthe piece of foam using a heater; applying a quantity of adhesive withan adhesive applicator directly to the heated top surface of the pieceof foam to improve wet tack of the adhesive and increase bond strength;wherein the adhesive applicator applies a high solids adhesive having60% or greater solids content; and adhering the top surface of the foampiece to a second foam piece before the adhesive has dried.
 2. Themethod of foam assembly of claim 1 wherein the step of applying thequantity of adhesive comprises roll coating the top surface.
 3. Themethod of claim 2 wherein the step of roll coating is achieved by anadhesive roller system comprising a primary roller which rolls overadhesive in a trough and applies the adhesive to the top surface of thefoam, a secondary roller, and a support roller.
 4. The method of foamassembly of claim 1 wherein the adhesive applicator applies a highsolids adhesive having 60-80% solids.
 5. The method of foam assembly ofclaim 1 wherein the step of heating the surface comprises heating thesurface of the foam to a temperature of approximately 220-300 F.
 6. Themethod of foam assembly of claim 1 wherein the heater is a convectionheater.
 7. The method of foam assembly of claim 1 further comprising thestep of compressing the foam and the second foam piece together.
 8. Themethod of foam assembly of claim 1 wherein the foam is a viscoelasticfoam.
 9. The method of foam assembly of claim 1 wherein the foam is apolyurethane core foam.
 10. The method of claim 1 further comprising thestep of vacuum packaging the adhered foam piece and second foam piece.11. The method of claim 1 further comprising the step of allowing thequantity of adhesive to dry after the step of adhering the top surfaceof the foam piece to the second foam piece.
 12. The method of claim 1wherein the step of adhering the top surface of the foam piece to asecond foam piece is performed within one minute from the step ofapplying the quantity of adhesive.